Portable breathing apparatuses of this kind are used for example by divers, by fire fighters when fighting fires or generally whenever air is charged with noxious substances which make unaided breathing impossible. Portable breathing apparatuses usually consist of one or two metal bottles or tanks which are carried for example on the back of the user and in which a highly compressed oxygen gas mixture at a pressure of for example 350 bar is contained. This oxygen gas mixture is designated below, for the sake of simplification, as breathing air, gas, pressurized gas, or simply as air. The breathing air is delivered from the bottles via a shut-off valve and breathed in by the user by means of a so-called demand valve located in a second stage regulator.
Typically, second stage regulators constitute the second of two stages of gas pressure regulation between a pressurized air source (e.g. the one or more tanks of compressed gas) and the respiratory system of a user. As conventionally known, a first stage regulator is operatively connected to the pressurized air source and delivers gas at an intermediate pressure (approximately 150 pounds per square inch (psi) over ambient pressure) to the second stage regulator. A function of the second stage regulator is to then deliver the intermediate pressure gas to the user at a breathable pressure in response to inhalation by the user.
A typical second stage regulator includes a housing, a regulator valve assembly mounted in the housing, a mouthpiece for communicating with the user, and an exhaust valve for expelling exhaled gas. Generally, a typical regulator valve assembly includes a tube sealed to the housing and having an inlet operatively connected to the first stage regulator, a valve orifice mounted in the inlet, a valve poppet mounted in the tube for movement between an open and a closed position with respect to the valve orifice, and a valve seat mounted at the end of the valve poppet. The tube further includes an opening for discharging the pressurized gas into the housing.
In operation, pressurized gas traveling from the first stage regulator passes through the valve orifice of the inlet and against the valve seat mounted at the end of the poppet. The pressure differential between upstream and downstream of the regulator valve assembly is approximately 150 psi. The pressure downstream of the regulator valve assembly is ambient pressure, while the pressure of the gas flow traveling from the first stage regulator is 150 psi over ambient. Traditional second stage regulators employ a mechanical biasing member to help counteract the effect of the pressure differential across the regulator valve assembly and acting on the frontal area of the valve seat. The mechanical biasing member commonly used is a spring. To counteract the difference in pressure, a relatively strong spring is needed to maintain the valve poppet in the closed position during operation. The spring acts on the valve poppet causing the valve seat to compress against the valve orifice (i.e. the closed position) until air is required by the user.
It is also known to use a valve poppet having a longitudinal passage extending through the valve poppet which enables the gas flow to travel through the valve poppet and to act on the backside of the valve poppet to assist in maintaining the valve poppet in the closed position. For example, U.S. Pat. No. 5,549,107 was issued to Garraffa et al. on Aug. 27, 1996 for a “Second Stage Scuba Diving Regulator.” However, known regulators using a valve poppet with a longitudinal passage still require a mechanical biasing member to help maintain the valve poppet in the closed position. Such known valve poppets have a backside area that is smaller than the frontal area, and are only able to provide partial force compensation thereby requiring the assistance of a mechanical biasing member.
A disadvantage of using a mechanical biasing member such as a spring to maintain the valve poppet in the closed position is that at the time of manufacturing, each second stage regulator must be checked to ensure that second stage regulator is properly adjusted with respect to the spring. An adjustment is commonly necessary due to the variability of spring constants inherent in any mass produced spring. Spring constants are likely to vary due to changes in material composition, inconsistent temperature changes during manufacturing of the spring, or differences in the manufacturing process itself. In addition, overtime, the repeated use of a second stage regulator (e.g. the continual compressing and relaxing of the spring during operation of the second stage regulator) may cause fatigue in the spring that could require a readjustment of the second stage regulator at a later time.
Accordingly, it would be advantageous to provide a second stage regulator that does not require adjustments at the time of manufacture to compensate for possible spring constant irregularities present in mass produced springs. It would further be advantageous to provide a second stage regulator that does not require a user to make adjustments to the second stage regulator with regard to the mechanical biasing member controlling the position of the valve poppet. It would further be desirable to provide a second stage regulator having a regulator valve assembly that functions smoother than a second stage regulator that employs a mechanical biasing member to control the positioning of the valve poppet. It would further be advantageous to provide a second stage regulator having a regulator valve assembly that eliminates the use of a mechanical biasing member to counteract the intermediate pressure existing at the inlet of the second stage regulator and maintain the valve poppet in a closed position. It would further be desirable to provide a second stage regulator that employs a pneumatically controlled regulator valve assembly.
To provide a reliable, widely adaptable second stage regulator with an improved regulator valve assembly that prevents the above referenced and other problems would represent a significant advance in the art.